The present invention relates generally to sound localization. Calculation of a multisensor time delay is disclosed.
For many audio signal processing applications, it is very useful to localize sound. Sound may be localized by precisely measuring the time delay between sound sensors that are separated in space and that both receive the sound. One of the important cues used by humans for localizing the position of a sound source is the Interaural Time Difference (ITD), that is, the difference in time of arrival of sounds at the two ears, which are sound sensors separated in space. ITD is usually computed using the algorithm proposed by Lloyd A. Jeffress in xe2x80x9cA Place Theory of Sound Localization,xe2x80x9d J. Comp. Physiol. Psychol., Vol. 41, pp. 35-39 (1948), which is herein incorporated by reference.
FIG. 1 is a diagram illustrating the Jeffress algorithm. Sound is input to a right input 102 and a left input 104. A spectral analysis 106 is performed on the two sound sources, and the outputs from the spectral analysis subsystems are input to cross correlator 108 which includes an array of delay lines and multipliers that produce a set of correlation outputs. This approach is conceptually simple, but requires many computations to be performed in a practical application. For example, for sound sampled at 44.1 kHz, with a 600-tap spectral analysis, and a 200-tap cross-correlator size (number of delay stages), it would be necessary to perform 5.3 Billion multiplications/second.
In order for sound localization to be practically included in audio signal processing systems that would benefit from it, it is necessary for a more computationally feasible technique to be developed.
An efficient method for computing the delays between signals received from multiple sensors is described. This provides a basis for determining the positions of multiple signal sources. The disclosed computation is used in sound localization and auditory stream separation systems for audio systems such as telephones, speakerphones, teleconferencing systems, and robots or other devices that require directional hearing.
It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, a method, or a computer readable medium such as a computer readable storage medium or a computer network wherein program instructions are sent over optical or electronic communication links. Several inventive embodiments of the present invention are described below.
In one embodiment, determining a time delay between a first signal received at a first sensor and a second signal received at a second sensor includes analyzing the first signal to derive a plurality of first signal channels at different frequencies and analyzing the second signal to derive a plurality of second signal channels at different frequencies. A first feature detected that occurs at a first time in one of the first signal channels. A second feature is detected that occurs at a second time in one of the second signal channels. The first feature is matched with the second feature and the first time is compared to the second time to determine the time delay.
These and other features and advantages of the present invention will be presented in more detail in the following detailed description and the accompanying figures which illustrate by way of example the principles of the invention.